Daena was the eldest daughter of Aegon III, and was born around 145 AL to unknown mother from the House Velaryon. At a early age, Daena was to marry her elder brother Baelor I, by her father. Daena and Baelor marriage was an very unhappy one, as her brother refused to consumate their marriage.

After the death of her elder brother Daeron I in Dorne, her husband Baelor took the throne and was named king and had his marrige with Daena anulled. Baelor, who still trouble having lustful thoughts towards his sisters, had Daena and his two other sisters Rhaena and Elaena locked in a chamber in the Red Keep, which became known has the Maidenvault and Daena along with her sisters were called the Princesses in the Tower. She and her two younger sisters were only 16, 14 and 11 respectively. Daena's cousin, then known has Prince Aegon IV, was not under any prohibition and developed a fondness for his cousin Daena, despite his marriage to his own sister-wife Naerys. The two would conceive a child together. Baelor later discovered that his sister escaped from her vault, and, much to his embarrassment, that Daena was pregnant with another man's child. Daena refused to reveal the named of the father, from that day on she became known has Daena the Defiant.

Daena would later raise her only child by herself, whom she named Daemon. Daena wasn't openly known as Aegon IV's mistress, until he became king and gave their son their ancestral sword Blackfyre, thus acknowledging him has one of his bastards.

Daena like the rest of her siblings had their family's Valyrian looks. She was best described as willful, strong, and beautiful. She had long, thick, curly silver-gold hair that framed a heart shaped face, with the Targaryen-purple eyes. Daena greatly idolized her eldest brother king Daeron I and worshipped her father King Aegon III whom she often emulated. She wore only black in her early years, along with the three-headed dragon pendant that she inherited from her father. She would never take off, supposedly even when bathing and making love. After the wedding to her elder brother Baelor I, who failed to consummated their marriage, Daena decided to only wear white until the day she is bedded, in hopes of shaming her brother.

Daena herself was very tomboyish and very athletic, a skilled archer and expert horesback rider. She would often say "I was born to ride a dragon".